In general, TTL (Through The Lens) flash exposure, the amount of light emitted from an auxiliary light source is determined by photometering reflect light from a film surface. However, since different types of films have different reflectances, the amount of light emitted which is determined on the basis of reflect light may become unstable. A digital single-lens reflex camera which uses an image sensing device in place of a film cannot virtually use this scheme because almost no reflect light can be obtained from the image sensing device.
The present applicant has proposed a camera system to solve this problem (Japanese Patent Laid-Open No. 9-61883). This camera system performs preliminary light emission toward an object and photometers reflect light from the object upon preliminary light emission by using a first photometry means. At the same time, the camera system photometers direct light upon preliminary light emission by using a second photometry means, and performs flash exposure in accordance with the photometric value of the reflect light and the photometric value of the direct light.
A compact digital camera has no mirrors like those in a single-lens reflex camera, and hence can perform flash exposure by directly using a CCD for image sensing operation. Patent reference 2 discloses an invention designed to perform flash exposure while eliminating the influence of flicker from a fluorescent lamp by photometering reflect light upon preliminary light emission only once after setting the shutter speed of an electronic shutter associated with a CCD to 1/1500.
In a press conference or wedding ceremony, many cameramen take many photographs of one object. Assume that while a first camera system is executing preliminary light emission and photometry, a second camera system executes main light emission. In this case, the first camera system cannot correctly perform photometry upon self preliminary light emission.
In addition, as described above, if the second camera system is a camera system designed to perform preliminary light emission, not only main light emission from another camera system but also preliminary light emission from another camera system may overlap preliminary light emission from the first camera system. This further increases the probability that photometry cannot be correctly performed. Obviously, if the first camera system is influenced by light emission from another camera system, underexposure occurs relative to a proper value.
As in the invention disclosed in Japanese Patent Laid-Open No. 10-32750, according to a method of photometering preliminary light emission only once upon setting the shutter speed to 1/1500, if another camera system emits light at the instant of photometry, the influence of the light emission cannot be reduced.